| Re: summation problem [message #24529] |
Thu, 05 April 2001 08:00  |
Paul van Delst
Messages: 364
Registered: March 1997
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Senior Member |
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Jaco van Gorkom wrote:
>
> Manish wrote:
> ...
>> I have a program which produces an array of values of sunlight flux during
>> the day. Unfortunately, it produces crazy numbers before the sunrises and
>> after it sets(as expected). I'm summing the values throughout the day to
>> get a total integrated day flux, but here's the problem - is there a way of
>> telling the TOTAL function to ignore negative numbers and NaN numbers?
>
> Yes, there is a way:
> IDL> test = [0,-1,3,4,]
> IDL> print, total(test>0,/nan)
> 7.00000
> % Program caused arithmetic error: Floating illegal operand
>
> The 'illegal operand' error appears to be harmless, caused by comparing test>0:
> IDL> print, test>0
> 0.00000 0.00000 3.00000 4.00000 NaN
> % Program caused arithmetic error: Floating illegal operand
Harmless maybe, but I for one don't like seeing illegal operand errors, let alone ignoring
them. What if you add some code that tries to take the log of a -ve number, see the same
error and shrug it off?
Why not do a
loc_finite = WHERE( FINITE( test ) EQ 1, count_finite )
IF ( count_finite GT 0 ) THEN $
sum = TOTAL( test[ loc_finite ] > 0.0 ) $
ELSE $
sum = !VALUES.F_NAN ; Or some other suitable flag
??
IDL> print, sum
7.00000
Oh, and make sure you set !EXCEPT = 2 in your idl setup file. That'll learn ya to remove
errors from your code :o)
paulv
--
Paul van Delst A little learning is a dangerous thing;
CIMSS @ NOAA/NCEP Drink deep, or taste not the Pierian spring;
Ph: (301)763-8000 x7274 There shallow draughts intoxicate the brain,
Fax:(301)763-8545 And drinking largely sobers us again.
paul.vandelst@noaa.gov Alexander Pope.
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| Re: summation problem [message #24548 is a reply to message #24529] |
Thu, 05 April 2001 05:32  |
Manish
Messages: 20
Registered: April 2001
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Junior Member |
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Nice one mate, worked a treat.
Thanks,
Manish
"Jaco van Gorkom" <j.c.van.gorkom@fz-juelich.de> wrote in message
news:3ACC53E1.A396D87C@fz-juelich.de...
> Manish wrote:
> ...
>> I have a program which produces an array of values of sunlight flux
during
>> the day. Unfortunately, it produces crazy numbers before the sunrises
and
>> after it sets(as expected). I'm summing the values throughout the day
to
>> get a total integrated day flux, but here's the problem - is there a way
of
>> telling the TOTAL function to ignore negative numbers and NaN numbers?
>
> Yes, there is a way:
> IDL> test = [0,-1,3,4,!values.f_nan]
> IDL> print, total(test>0,/nan)
> 7.00000
> % Program caused arithmetic error: Floating illegal operand
>
> The 'illegal operand' error appears to be harmless, caused by comparing
test>0:
> IDL> print, test>0
> 0.00000 0.00000 3.00000 4.00000 NaN
> % Program caused arithmetic error: Floating illegal operand
>
>> I guess this is a simple problem, but would appreciate any help
> It is simple enough, but only once you know the solution.
>
> cheers,
> Jaco
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| Re: summation problem [message #24549 is a reply to message #24548] |
Thu, 05 April 2001 04:15 |
Jaco van Gorkom
Messages: 97
Registered: November 2000
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Member |
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Manish wrote:
...
> I have a program which produces an array of values of sunlight flux during
> the day. Unfortunately, it produces crazy numbers before the sunrises and
> after it sets(as expected). I'm summing the values throughout the day to
> get a total integrated day flux, but here's the problem - is there a way of
> telling the TOTAL function to ignore negative numbers and NaN numbers?
Yes, there is a way:
IDL> test = [0,-1,3,4,!values.f_nan]
IDL> print, total(test>0,/nan)
7.00000
% Program caused arithmetic error: Floating illegal operand
The 'illegal operand' error appears to be harmless, caused by comparing test>0:
IDL> print, test>0
0.00000 0.00000 3.00000 4.00000 NaN
% Program caused arithmetic error: Floating illegal operand
> I guess this is a simple problem, but would appreciate any help
It is simple enough, but only once you know the solution.
cheers,
Jaco
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| Re: summation problem [message #24624 is a reply to message #24529] |
Thu, 05 April 2001 09:26 |
Jaco van Gorkom
Messages: 97
Registered: November 2000
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Member |
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Paul van Delst wrote:
> Jaco van Gorkom wrote:
>> Manish wrote:
>> ...
>>> I have a program which produces an array of values of sunlight flux during
>>> the day. Unfortunately, it produces crazy numbers before the sunrises and
>>> after it sets(as expected). I'm summing the values throughout the day to
>>> get a total integrated day flux, but here's the problem - is there a way of
>>> telling the TOTAL function to ignore negative numbers and NaN numbers?
>>
>> IDL> print, total(test>0,/nan)
>> 7.00000
>> % Program caused arithmetic error: Floating illegal operand
>>
>> The 'illegal operand' error appears to be harmless, caused by comparing test>0:
>
> Harmless maybe, but I for one don't like seeing illegal operand errors, let alone ignoring
> them. What if you add some code that tries to take the log of a -ve number, see the same
> error and shrug it off?
That is *exactly* what I'd do: shrug it off! The log of a -ve number gives me
-Inf as a
result, which will propagate through any calculation to be NaN, Inf, or -Inf.
Just another
missing data point.
> loc_finite = WHERE( FINITE( test ) EQ 1, count_finite )
> IF ( count_finite GT 0 ) THEN $
> sum = TOTAL( test[ loc_finite ] > 0.0 ) $
> ELSE $
> sum = !VALUES.F_NAN ; Or some other suitable flag
Of course I see your point. I would probably implement a FINITE() check if I
were writing a
full program, but the annoying special-case programming for when WHERE() returns
-1 held me
back here.
On second thought: WHERE() could only return -1 for a day without sunrise...
groetjes,
Jaco
> ...
> Oh, and make sure you set !EXCEPT = 2 in your idl setup file. That'll learn ya to remove
> errors from your code :o)
Geez! Thanks for pointing that out! This solves everything Manish: !EXCEPT = 0.
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